The present invention relates to the separation of foam into liquid and air and more particularly to the control of the separating the liquid and gas phase of foam.
Foam consists of a large number of air bubbles having thin walls of liquid. In foaming liquids, the presence of surfactants in the liquid causes the liquid to resist draining out of the bubble walls. The surface tension of the liquid films resists the rupturing of the walls. As a result of gravity and other driving forces, however, the liquid will slowly drain from the bubble wall until it becomes sufficiently thin that the bubble walls become brittle and rupture.
Many fields require the separation of foam into liquid and air, such as biotechnology in controlling foam in bubble columns and of ink jet technology in controlling foam in the fluid system ink supply tank.
Foam is created in continuous ink jet fluid systems due to the fact that not all ink drops are used for printing. The unused ink drops are returned to the fluid system under vacuum through a catcher. The ink and air are mixed at the catcher and in the fluid lines. which return the two phase flow (foam) to the ink supply tank. In some cases, the foam can build up in the ink supply tank and eventually be evacuated into the vacuum system. Damage can then occur to the vacuum system.
Some prior art means of controlling foam, or defoamers, exist. For example, chemicals can be added to the fluid which lowers the stability of the bubble walls. However, these can have an undesirable effect on the performance of the liquid in an ink jet printing application, by changing the ink formulation and parameters.
Mechanical defoamers, such as described in U.S. Pat. No. 4,657,677, issued to Roubicek et al, break the foam by stretching and deforming the bubble walls until they rupture. This might be done by means of a rotating disk, cones or other means, or to some extent by the flow of the foam down a ramp. While non-rotating methods do not break the foam rapidly enough in all cases given the size design constraints. rotating designs require moving parts which may be subject to failure and the cost of an extra motor.
Thermal defoamers heat the fluid above a critical temperature at which drainage of the fluid from the bubble walls increases dramatically. In ink jet systems, as well as other systems, the temperatures required can cause unacceptable break down of the fluid.
It is seen, therefore, that it would be desirable to have an improved means for separating the liquid and gas phase of foam.
The present invention provides an improved mechanical means of separating the liquid and gas phases of foam. The two phase flow separator of the present invention can be applied for use in any field which requires the separation of foam into liquid and air.
In accordance with one aspect of the present invention, an apparatus is provided for separating the liquid and gaseous components of a foamy mixture. The apparatus comprises a filter means through which the liquid portion of the foam can pass and through which the gaseous component cannot pass, unless a pressure differential across the filter exceeds the bubble point of the filter. First means are provided to supply the foam to a first side of the filter means. Additional means are provided to remove the liquid component of the foam from the second side of the filter, and the gaseous component of the foam from the first side of the filter. A pressure differential is established between the two sides of the filter to cause the liquid component of the foam to pass through the filter; but the pressure differential across the filter is prevented from exceeding the bubble point of the filter to prevent the gaseous component of the foam from passing through the filter.
Other objects and advantages of the invention will be apparent from the following description and the appended claims.